Aluminum

Extracted from: A Buyer's Guide for Aluminum Metal Powders by Ken L. Kosanke PGII Bulletin 27 & 28 November, 1981 & December, 1982 [Back issues single and bound of the Pyrotechnics Guild International Inc. Bulletin are available from the PGII. www.pgi.org ] [scanned and you know what that means!] 1) The number one question concerns the definition of the very general descriptive terms -- dark, light and bright. I think these are poor terms and their use should be avoided. They are much too general and can mean quite different things to various people. These differences (between kinds of aluminum powders) can be very significant. Even subtle differences, not detectable by eye or feel, can produce significantly different pyrotechnic effects (more on this later). Dark USUALLY refers to very fine flake aluminum, with finer flake USUALLY appearing darker. This is a consequence of light reflecting off the more numerous irregular particle surfaces. However, an exception is "German dark" aluminum. Here most of the dark color is from the presence of carbon, resulting from its manufacturing process more on this later). There are at least three grades of German dark, all appearing quite dark, but all having different particl sizes. Obviously in this case, darkness of appearance is no guide t particle size. It has also been reported in the literature that some manufacturers add carbon black to their products. Again, darkness is no guide to particle size. To MOST pyrotechnists, bright, not light, is the opposite of the attribute dark. USUALLY, bright refers to flake aluminums, but the flakes are large enough (if free of carbon) to appear shiny (bright). Bright flake aluminum can still be very fine and very reactive. Light USUALLY refers to atomized or finely ground aluminums. The particles of aluminum have more of a 3-dimensional character than flakes. Unfortunately, light atomized aluminum can be as dark appearing as dark flake aluminum. Confusion can be avoided by substituting more descriptive terms, such as "flake" and "atomized", along with an indication of particle size, for the ambiguous dark, light and bright. Possibly the one exception I make is the use of the term flitters, which are very large flakes usually in the range of 8 to 14 mesh.